The present invention relates to a seat belt retractor mounted on a vehicle, such as automobile, for controlling unwinding and winding of a seat belt for restraining and protecting a passenger and, more specifically, the invention relates to a seat belt retractor for restraining and protecting a passenger more reliably by controlling tension of the seat belt based on the conditions outside the vehicle or the operating conditions of the seat belt.
The seat belt device that has been mounted conventionally on the vehicle, such as automobile, protects a driver and passenger from being jumped out from the seat in case of emergency such that an abrupt deceleration is applied to the vehicle in the event of a collision or the like by restraining the driver or passenger with a seat belt.
The seat belt device of this type is provided with a seat belt retractor for winding the seat belt. The seat belt retractor comprises energy application means, such as flat spiral spring, for urging a reel for winding the seat belt at all the time in the normal winding direction. The seat belt is wound on the reel by the energy applied by the energy application means when not in use. In contrast, in use, the seat belt is unwound against the energy applied by the energy application means and worn by the passenger. The seat belt retractor prevents unwinding of the seat belt in case of emergency as stated above by actuating locking means to prevent the reel from rotating in the unwinding direction. This ensures that the seat belt restrains and protects the passenger in case of emergency.
In the conventional seat belt device of the type described above, an almost constant tension is applied to the seat belt by the energy from the energy application means when the seat belt is in use. Therefore, the seat belt retractor always acts in the same manner independently of the conditions of the vehicle itself and surrounding the vehicle. However, although the conventional seat belt device ensures protection of the passenger in case of emergency as stated above, it can not be said that the seat belt is controlled comfortably for the passenger in the case other than emergency as stated above. In addition, it is preferable to protect the passenger more positively by restraining the passenger securely in case of emergency.
A passenger restraining and protecting system is provided in Japanese Unexamined Patent Publication (KOKAI) No. 9-132113, wherein the restraint and protection of the passenger are carried out more efficiently and more comfortably for the passenger by controlling the rotation of the reel of the seat belt retractor and adjusting the belt tension by a motor with consideration of the conditions between the vehicle itself and outer objects.
On the other hand, when the locking means of the seat belt retractor is actuated in case of emergency and prevents the reel from rotating in the unwinding direction as stated above, the passenger tends to move forward by an inertial force and is subjected to a significant impact by the seat belt. Therefore, a seat belt retractor comprising a belt load limiting mechanism (EA mechanism) is also proposed, wherein a torsion bar is provided between the reel and the locking means in order to protect the passenger from the impact so that the torsional deformation of the torsion bar absorbs the impact energy and relieves the impact applied to the passenger.
Since a large number of components is used in the belt tension control mechanism in the passenger restraining and protecting system disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 9-132113, and these components perform complicated actions, the seat belt retractor becomes significantly large size and the operational control is complicated.
However, the space in the interior of the vehicle where the seat belt retractor is mounted is limited, and is quite small, and the space for mounting the seat belt retractor is strictly limited when considering the habitability of the interior of the vehicle. Therefore, it is preferable to provide a seat belt retractor that can accommodate the strict limitation of the mounting space by downsizing it as small as possible, while allowing control of the belt tension based on the conditions between the vehicle itself and the outer objects.
In addition, since the operational control of the belt tension control mechanism is quite complicated, the drive control of the motor is not simple and, in addition, the drive circuit of the motor is complicated and costly.
In view of such conditions, it is an object of the invention to provide a seat belt retractor, wherein the structure of the belt tension control mechanism is simplified by reducing the number of components as small as possible, and the control of the belt tension control mechanism is reliable and simple.
Further objects and advantages of the invention will be apparent from the following description of the invention.
In order to overcome the problems described above, a seat belt retractor according to a first aspect of the invention comprises a reel for winding a seat belt, reel urging means for urging the reel in the seat belt winding direction, locking means provided between a frame and the reel for allowing rotation of the reel in a normal condition, and preventing the rotation of the reel in the belt unwinding direction when necessary, and a belt tension control mechanism for controlling the belt tension of the seat belt. The belt tension control mechanism comprises a motor for generating a rotational torque, a power transmission path having an OFF-state in which the rotational torque is not transmitted between the motor and the reel, and an ON-state in which a rotational torque is transmitted between the motor and the reel, and a power transmission path switching mechanism for selectively switching the power transmission path between the ON-state and the OFF-state. The power transmission path switching mechanism is actuated by the rotational torque of the motor.
In a second aspect of the invention, the power transmission path includes a power transmission gear mechanism; the power transmission path switching mechanism includes a switch gear axially movable for controlling the operation of the power transmission path switching mechanism; and the gear of the power transmission gear mechanism and the switch gear are both formed in helical gears and are engaged with respect to each other. When the gear of the power transmission gear mechanism is rotated by the rotational torque of the motor, the switch gear is rotated, and the axial tension generated in the axial direction by the rotation of both gears moves the switch gear in the axial direction, thereby actuating the power transmission path switching mechanism and setting the power transmission path into the ON-state.
In a third aspect of the invention, the power transmission path father includes a speed reducing mechanism for reducing the speed of the rotation of the motor transmitted from the power transmission gear mechanism and transmitting it to the reel; and the speed reducing mechanism includes a sun gear, a ring-shaped internal gear rotatably mounted and having ratchet teeth on the outer periphery thereof and internal teeth on the internal periphery thereof, a planetary gear to be engaged with the sun gear and with the internal gear, a carrier for rotatably supporting the planetary gear and transmitting the rotation thereof to the reel, and a speed reducing gear provided so as to rotate with the sun gear as a single unit for receiving the rotation of the motor transmitted from the power transmission gear mechanism. The power transmission path switching mechanism further comprises a stop lever rotatable between a non-engaging position in which the stop lever is not engaged with the ratchet teeth and the engaging position in which the stop lever is engageable with the ratchet teeth, and a plunger for placing the stop lever to the non-engaging position in the normal state in which the switch gear does not move in the axial direction to allow the free rotation of the internal gear, and for preventing the rotation of the internal gear when actuated by the movement of the switch gear in the axial direction, by placing the stop lever to the engaging position so that the stop lever is engaged with the ratchet teeth. The power transmission path is set to the OFF-state when the internal gear is free to rotate, and is set to the ON-state when the internal gear is prevented from rotating.
In a fourth aspect of the invention, the power transmission path includes a power transmission gear mechanism, and the power transmission path switching mechanism includes a control lever rotatable for controlling the operation of the power transmission path switching mechanism. When a gear of the power transmission gear mechanism is rotated by the rotational torque of the motor, the power transmission path switching mechanism is actuated by the rotation of the rotatable control lever so that the power transmission path is set to the ON-state.
In a fifth aspect of the invention, the power transmission path further comprises a speed reducing mechanism for reducing the speed of the rotation of the motor transmitted from the power transmission gear mechanism and transmitting it to the reel. The speed reducing mechanism comprises a sun gear, a ring-shaped internal gear rotatably mounted and having ratchet teeth on the outer periphery and internal teeth on the inner periphery, a planetary gear to be engaged with the sun gear and the internal gear, a carrier for rotatably supporting the planetary gear and transmitting the rotation thereof to the reel, and a speed reducing gear provided so as to rotate with the sun gear as a single unit for receiving the rotation of the motor transmitted from the power transmission gear mechanism. The power transmission path switching mechanism further comprises a stop lever rotatable between a non-engaging position in which the stop lever is not engaged with the ratchet teeth and an engaging position in which the stop lever is engageable with the ratchet teeth, so that, in the normal state in which the control lever does not rotate, the stop lever is placed into the non-engaging position to allow the free rotation of the internal gear, and when the control lever is rotated, the stop lever is placed to the engaging position and engaged with the ratchet teeth to prevent the rotation of the internal gear. In the state in which the internal gear is free to rotate, the power transmission path is set to OFF-state and in the state in which the rotation of the internal gear is prevented, the power transmission path is set to the ON-state.
In addition, in a sixth aspect of the invention, the control lever may be formed of a lever spring having a prescribed resiliency.
In a seventh aspect of the invention, the planetary gear comprises a large planetary gear having a large diameter and engaging the sun gear at all the time, and a small planetary gear having a diameter smaller than the large planetary gear provided so as to rotate with the large planetary gear as a single unit. The small planetary gear engages the internal teeth of the internal gear at all the time.
In an eighth aspect of the invention, the speed reducing mechanism is provided with a transmitted torque limiting mechanism that discontinues transmission of a power when a power transmission torque is equal to or higher than a prescribed value.
In a ninth aspect of the invention, the transmitted torque limiting mechanism is composed of a supporting portion of the planetary gear that is ruptured when the power transmission torque is equal to or higher than the prescribed value.
In the tenth aspect of the invention, the power transmission gear mechanism includes a belt power transmission mechanism comprising first and second pulleys, and an endless belt looped between the first and the second pulleys. The belt power transmission mechanism is provided with a transmitted torque limiting mechanism that discontinues power transmission by generating a slip between the endless belt and at least one of the first and the second pulleys when a power transmission torque is equal to or higher than a prescribed value.
In an eleventh aspect of the invention, a seat belt retractor comprises at least a reel for winding a seat belt, locking means provided between a frame and the reel for allowing rotation of the reel in a normal condition and actuated to prevent the rotation of the reel in a belt unwinding direction when necessary, and a belt tension control mechanism for controlling the belt tension of the seat belt. The belt tension control mechanism comprises a motor for generating a rotational torque, a power transmission path for transmitting a rotational torque between the motor and the reel, vehicle""s emergency state detecting means for detecting the emergency state of the vehicle and sending a signal, and motor drive control means for driving the motor in the belt winding direction for a first preset time period according to the signal from the vehicle""s emergency state detecting means to restrain the passenger, then stopping the operation of the motor, and when the prescribed conditions are satisfied after the motor has stopped, driving the motor again in the belt winding direction additionally for a second preset time period.
In addition, in a twelfth aspect of the invention, the vehicle""s emergency state detecting means detects that the vehicle is in the emergency state when it determines that three conditions, that is, a condition that the speed of the vehicle is equal to or higher than the first fixed speed, a condition that the speed of depression of the brake pedal is equal to or higher than a fixed speed of depression, and a condition that a deceleration of the vehicle is equal to or higher than the first fixed deceleration, are all satisfied.
In addition, in a thirteenth aspect of the invention, the vehicle""s emergency state detecting means detects that the vehicle is in the emergency state when a condition that the speed of the vehicle is equal to or higher than the first fixed speed is determined to be satisfied, when a condition that the speed of depression of the brake pedal is equal to or higher than a fixed speed of depression is determined to be satisfied, or when a condition that the acceleration of the vehicle is equal to or higher than the first fixed acceleration which is a positive value, or is equal to or lower than the second fixed acceleration which is a negative value is determined to be satisfied.
In a fourteenth aspect of the invention, the prescribed condition is one of a condition that the vehicle has stopped, a condition that the speed of the vehicle is equal to or lower than the second fixed speed, a condition that the deceleration of the vehicle is equal to or lower than a second fixed deceleration, and a condition that a time elapsed from a moment when the operation of the motor is stopped is equal to or longer than a third preset time period.
In addition, in a fifteenth aspect of the invention, the motor is driven in the belt unwinding direction for the third preset time period after the motor is driven in the belt winding direction for the second preset time period.
In the seat belt retractor in this arrangement according to the present invention, the ON and OFF-states of the power transmission path between the reel and the motor is selectively switched by the power transmission switching mechanism operationally controlled by a driving force of the motor. In other words, when the motor is not in operation, the power transmission path switching mechanism is not actuated, the power transmission path is set to OFF-state, and thus a rotational torque is not transmitted between the motor and the reel. Therefore, when the seat belt is drawn out and the reel rotates in the belt unwinding direction, or when the reel rotates in the belt winding direction during belt winding operation after the seat belt is unwound, the rotation of the reel is not transmitted to the motor and the power transmission path switching mechanism, and the motor and the power transmission path switching mechanism are not affected by the rotation of the reel.
When the motor is in operation, the rotational torque of the motor actuates the power transmission path switching mechanism, the power transmission path is set to the ON-state, and the rotational torque is transmitted between the motor and the reel. Therefore, the rotational torque of the motor is transmitted to the reel via the power transmission path switching mechanism to rotate the reel, and the winding and unwinding of the seat belt are carried out to control the belt tension. In this way, the belt tension is controlled to a prescribed value by the belt tension control mechanism actuated by the driving force of the motor.
In this case, since the ON and OFF-states of the power transmission path are controlled by the power transmission path switching mechanism operated by rotational torque of the motor, a specifically designed actuator driven by other motive power, such as electromagnetic solenoid or the like, for actuating the power transmission path switching mechanism is not required. Therefore, the power transmission path switching mechanism has less number of components and is simple in structure, and thus the cost is further reduced.
According to one aspect the invention, when a power transmission torque is equal to or higher than the prescribed value, the transmitted torque limiting mechanism discontinues transmission of a power. Accordingly, in case a power transmitted in case of an emergency is increased suddenly, the power transmission is stopped whereby a load of the motor itself is not linked to the reel side. Therefore, as described above, in the seat belt retractor having the EA mechanism on the reel side, the load of the motor itself is not linked to the EA mechanism. As a consequent, increase in load applied to the EA mechanism due to the load of the motor itself (EA load) is suppressed. In this case, according to the invention, the structure of the transmitted torque limiting mechanism is simple because the supporting portion of the planetary gear is constructed to be ruptured to discontinue transmission of the power when the power transmission torque is equal to or higher than the prescribed value.
In one aspect the invention, when the power transmission torque is equal to or higher than the prescribed value, a slip generated between the endless belt and the pulley discontinues the power transmission. Accordingly, as described above, even when the power transmitted increases suddenly, transmission of the power is discontinued, so that the high load of the motor itself is not linked to the reel side. Therefore, in the seat belt retractor including the EA mechanism on the reel side, the high load of the motor itself is not linked to the EA mechanism. Consequently, increase in the belt limiting load due to the high load of the motor itself can be controlled or suppressed.
In addition, in the above case, the component of the power transmission mechanism, such as a supporting portion of the planetary gear, is not ruptured when a power transmission torque is equal to or higher than the prescribed value, so that when a power transmission torque has lowered to the prescribed value or below, the component can be used repeatedly. Therefore, in the vehicle that can be driven freely even after occurrence of an emergency, such as a crush, when another emergency, such as a secondary crush occurs again while the vehicle is being driven to another location, such as a repair shop, the capability of the seat belt retractor to restrain the passenger by winding its seat belt by the motor may be fully exerted again.
According to one aspect of the invention, when the emergency state of the vehicle is detected, the motor is driven in the belt winding direction for the first preset time period to restrain the passenger. Then, when the prescribed conditions are satisfied after stoppage of the motor, the motor is driven again in the belt winding direction additionally for at least the second preset time period. Consequently, after the locking means is actuated by occurrence of the vehicle""s emergency and then the emergency state is eliminated, the actuation of the locking means is automatically released. Therefore, the passenger is released easily and more reliably from the state of secure restraint brought by the motor driven in the belt winding direction. In addition, it is not necessary to release the engagement between the tongue and the buckle every time as in the case of the conventional system any more, whereby the additional lock releasing operation to be made by the passenger can be eliminated.
Especially, in one aspect of the invention, only when three conditions are satisfied, the vehicle""s emergency state can be detected, so that the detection is performed in further detail and more accurately.
In one aspect of the invention, detection of the vehicle""s emergency state by the vehicle""s emergency state detecting means is made relatively easy since the vehicle""s emergency state detecting means detects that the vehicle is in the emergency state when the condition that the speed of the vehicle is equal to or higher than the first fixed speed is determined to be satisfied, when the condition that the speed of depression of the brake pedal is equal to or higher than a fixed speed of depression is determined to be satisfied, or when the condition that the acceleration of the vehicle is equal to or higher than the first fixed acceleration which is a positive value, or is equal to or lower than the second fixed acceleration which is a negative value is determined to be satisfied.
In one aspect of the invention, it is determined that the vehicle""s emergency state is eliminated when one of the conditions, i.e. the condition that the vehicle has stopped, the condition that the speed of the vehicle is equal to or lower then the second fixed speed, the condition that the deceleration of the vehicle is equal to or lower than the second fixed deceleration, and the condition that the time elapsed from the stoppage of the motor is equal to or longer than the third preset time period, is eliminated. Consequently, the operation of the locking means is automatically released at an earlier stage and more flexibly after the vehicle""s emergency state is eliminated.
In one aspect of the invention, after the vehicle""s emergency state is eliminated and the operation of the locking means is automatically released, the seat belt is restored automatically to the state before the vehicle""s emergency state was detected. Consequently, the passenger need not perform the additional lock releasing operation, and what is more, the user can be released automatically from the restrained state.